DNA polymerase a is isolated as a protein-complex by affinity chromatography. The subunits are then separated by SDS gel electrophoresis. The proteins are in-gel digested. The peptides are separated by reversed phase HPLC. Molecular weight and sequence information obtained by MALDI, MALDI-PSD and MALDI-CID are then used to identify the protein in the S. ponbe database or for oligonucleotide probes for PCR and subsequent DNA sequencing experiments.